The present Invention relates, in general, to a novel laser device wherein the laser medium is pumped by microwave RF excitation at frequencies in the range of 8 to 12 GHz (X-band).
Radio-frequency sources in the 1 to 30 MHz frequency range have been used in prior art pumping systems for exciting mixtures of gases to generate lasing. Such systems typically utilize inductive or capacitive coupling to couple the RF energy into the lasing medium. U.S. Pat. No. 3,521,119 to AHMED is an example of one type of inductively coupled RF pumped laser while U.S. Pat. No. 3,748,594 to PUGH illustrates a capacitivety coupled system.
These prior art systems generally are incapable of coupling significant amounts of the RF energy into the lasing medium and thus tend to be rather inefficient. Also, these systems typically radiate significant amounts of RF energy which presents obvious radio frequency interference problems (RFI) and the resultant necessity for expensive and bulky shielding. Another problem with these systems is that they require metallic electrodes, sometimes in contact with the lasing medium, to couple the RF energy to the medium. Since many lasing media are extremely corrosive, the use of the electrodes severely limits the available lasing media to those which are the least corrosive. Also problems exist due to contamination of the lasing media by the electrodes.
Microwave excitation laser systems are known in the prior art. These systems have operated with frequencies of up to about 3 GHz. Efficiency and coupling problems exist with these devices necessitating the use of external fields and/or usual geometries. For example U.S. Pat. No. 3,602,837 to GOLDSBOROUGH discloses a microwave excited laser device wherein RF energy is supplied to a conductive band wrapped about a plasma tube located within an external magnetic field. The RF energy and the external field combine to produce standing waves within the lasing medium. U.S. Pat. No. 4,004,249 to KIKUCHI discloses a laser device wherein an optical waveguide is located within a microwave waveguide. The microwave waveguide includes a tapered "throat" portion in the vicinity of the optical waveguide which acts to concentrate the electric field within the optical waveguide.
The present Invention provides a novel microwave excited laser device which operates at X-band RF frequencies (8-12 GHz) and which does not require the use of external fields or complicated geometries. The device does not require the use of electrodes and thus avoids the problems inherant with the use of electrodes. Very high coupling efficiencies are obtained.